The invention relates to a method of producing, on a circular knitting machine having a rotatable needle cylinder, knit fabrics having combed-in fibers and a preselected fiber density, the method comprising the steps of delivering an amount of fibers synchronous with the needle cylinder rotary speed to a teasing cylinder rotating at high speed, yielding fibers from said teasing cylinder to a comb-in zone and transfering fibers in the comb-in zone to the needles without the needles contacting the teasing cylinder. The invention further relates to a knitting machine on which this method can be carried out.
In methods and circular knitting machines of this kind (U.S. Pat. Nos. 4,458,506 and 4,546,622 the fibers, in contrast to conventional methods and circular knitting machines U.S. Pat. No. 3,709,002 are combed contactlessly into the needle hooks, the term "contactlessly" meaning that the needle hooks do not pass through teasing hooks. The transfer of the fibers to the comb-in zone is performed as in circular knitting machines with conventional combs under conditions synchronous with the rotation of the needle cylinder. The term, "synchronous conditions", is to be understood to mean that, at any constant rotatory speed of the needle cylinder, the fibers are always delivered to the comb-in zone at a preselected, constant amount of fibers per unit time, so as to produce goods having a preselected, constant fiber density. On the other hand, the amount of fiber fed to the comb-in zone changes synchronously in the case of changes in the needle cylinder rotatory speed, in order that, in the event of reductions or increases in the needle cylinder rotatory speed, correspondingly less or more fibers will be delivered to the comb-in zone, thereby assuring that the preselected fiber density will be achieved at any rotatory speed of the needle cylinder, i.e., especially during the execution of start and stop cycles. If the feed of fiber to the teasing cylinder by means of feed rolls, for example, "synchronous conditions" means that the feed rolls and the needle cylinder are driven from a single, main drive through gears, belts, rollers or the like, so that the ratio of their rotatory speeds is the same at all rotatory speeds of the needle cylinder, and that, independently thereof, the teasing cylinder is driven always at the same high rotatory speed at all needle cylinder speeds.
Experiments on such circular knitting machines with contactless fiber feed have surprisingly shown that, during those phases in which the needle cylinder is subjected to abrupt changes of rotatory speed, such as is the case especially during the start and stop cycles and during "tip" operation, undesirable deviations from the preselected fiber density can result, which lead to thick and thin areas in the finished knit goods.
"Thick and thin areas" in this connection refers to those points in the finished goods at which the fiber density is lower or higher than the preselected fiber density. The length of the thick and thin areas appears to be dependent upon a number of factors, such as the length of time for which the needle cylinder is stopped, the duration of the braking or accelerating cycles of the needle cylinder until it reaches a full stop or the production speed, the fiber length, or the titer of the fibers.
The invention is addressed to the problem of improving the method and the circular knitting machine of the kind defined such that thick and thin areas will be largely avoided. In particular, those thick and thin areas are to be avoided such as can develop upon the abrupt braking of the needle cylinder to a stop, e.g., due to thread breakage or the like, or upon the acceleration of the needle cylinder from a full stop until it reaches the production speed.
The method of this invention is characterized by substantially maintaining constant the preselected fiber density also when abrupt changes of the rotary speed of the needle cylinder occur by at least momentarily feeding amounts of fibers which differ from the synchronous amount of fibers to the comb-in zone. A circular knitting machine for the production of knit goods with combed-in fibers comprises according to this invention a rotatable needle bearing needle cylinder, a card which has a means for feeding the fibers, a comb-in zone through which the needles pass for the purpose of contactless fiber pickup, and a teasing cylinder rotating at high speed which takes the fibers from the feed means and gives them to the comb-in zone, and a drive means for the synchronous driving of the needle cylinder and feed means. The card has a controller which becomes active upon abrupt changes in the rotary speed of the needle cylinder for the synchronous changing of the amount of fibers yielded to the comb-in zone.
The invention brings with it the surprising advantage that a great number of thick and thin areas can be prevented by the simple measure of feeding fewer fibers upon the abrupt braking of the needle cylinder, but more fibers upon the acceleration of the needle cylinder from a full stop, than would correspond to the synchronous amounts of fibers.
Additional advantageous features of the invention will be found in the subordinate claims.
The invention will now be further explained in conjunction with the appended drawing of a preferred embodiment.